Table 1.

Summary of the responses of chloroplast and chloroplast retrograde signalling to heat, and chloroplast-related plant heat tolerance.

	Plant System	Related Physiological Processes	Proteins or Signal Molecules [Ref.]
Part I: Chloroplast are sensitive to heat stress:
PSII	Plants	Photosynthesis	D1/D2 [12,13,14,15,16,17,18]
Protein translation system	Arabidopsis	Protein translation	EF-Tu [23,24,25], RPS1 [26]
Chlorophyll metabolism	Bentgrass Arabidopsis	Chlorophyll degradation Chlorophyll turnover	PPH [31] CHLG [32], CLD1 [33]
Dark reaction of photosynthesis	Plants	Photosynthesis	Rubisco and RCA [35,36,37]
Part II: Chloroplast retrograde signalling that responds to heat stress
1. Calcium ion concentration	Arabidopsis	Calcium signalling	CAS [39]
2. ROS	Plants Arabidopsis Plants		Singlet oxygen [41] β-cyclocitral [43] H2O2 [44]
3. Metabolic molecules	Chlamydomonas Arabidopsis	Tetrapyrrole metabolism Tocopherol and sulfur metabolism	Mg-Proto IX and hemin [47] Vitamin E-PAP-miR398 [48]
4. Components in chloroplast	Arabidopsis Arabidopsis Arabidopsis Arabidopsis	Chlorophyll biosynthesis Protein translation Transcription and plastid translation Protein phosphorylation	GUN5 [49] RPS1 [26] CIA2 [50] CK2 [51]
5. Components out of chloroplast	Arabidopsis Arabidopsis Arabidopsis, tomato et al. Arabidopsis	Maintaining signalling proteins/Heat Transcription factor Transcription factor/Heat Transcription factor	HSP90 [42,76] PTM-ABI4 [42] HSFA2 [26,42] HY5, GLKs [42]
Part III: Chloroplast proteins contribute to plant heat tolerance
1. HSPs  a. HSP100s      b. HSP70s      c. HSP60s      d. HSP40s     e. sHSPs	Arabidopsis, Tomato Arabidopsis Pepper Tomato Arabidopsis Creeping bentgrass Tall fescue Maize Chlamydomonas	Protein quality control Protein quality control   Protection of PSII, Rubisco Plastid transcription/PSII stabilization   Thermomemory Protection of photosynthetic protein Protection of photosynthetic protein	APG/ClpB3 [56,57], LeHSP100 [58] cpHsc70-1 [59] CaHSP60-6 [62] LeCDJ1 [60], LeCDJ2 [61] HSP21 [65] HSP26.8a [66] FaHSP17.8-CII [67] sHSP26 [69] HSP22E/F [70]
2. ROS related	Arabidopsis C. merolae Tomato	Regulation of MDH ROS-scavenging Melatonin biosynthesis	TRXL1 [71] APX [72] SlSNAT [73]
3. Protease	Arabidopsis	Protein quality control	FtsH11 [74]
4. Lipid metabolism	Sweet pepper	Glycerolipid biosynthesis	GPAT [75]